增加载荷分享的动力椎弓根螺钉固定器的稳定性及其意义

目的：比较增加载荷分享的动力椎弓根螺钉固定器（dynamic device,DD)与其相对的坚强固定器（rigid device,RD)的稳定性,并探讨动力固定器的生物力学作用。方法：在7例新鲜成人尸体T10－T4脊柱标本,模拟L1骨折后安放DD和RD,进行脊柱三维运动范围和前屈－压缩刚度测试。结果：DD与RD能在屈伸,侧弯运动方向上显著增加节段稳定性,使轴向旋转运动恢复至正常运动范围。DD比RD屈伸运动范围增加40％,前屈－压缩刚度减小24．1Nmm。结论：2种脊柱内固定器均能稳定所损的脊柱,但动力椎弓根螺钉固定器的设计可在不牺牲脊柱固定稳定性的前提下,增加载荷分享,减少应力遮挡和应力集中,符合弹性固定原则。

Stability analysis of an enhanced load sharing dynamic pedicle screw fixation device and its equivalent rigid device

Objectives To compare the stability of an enhanced load sharing dynamic pedicle screw fixation device with its equivalent rigid device and to evaluate biomechanical roles of the dynamic fixation. Methods A model of L 1 body fracture was produced on seven specimens of fresh adult cadaver spine from T 10 to L 4. Both dynamic and rigid devices were applied in the specimens to strength the injured level. Ranges of three dimensional movements and stiffness under flexion compression were measured in intact, injured and stabilized specimens. Results Both dynamic and rigid devices were found to provide significant stability for injured segment in flexion extension and lateral bending. In axial rotation, the devices could restore the stability to levels similar to those in an intact spine. Results indicated 40% increase in range of motion in flexion extension and 24 1 Nmm reduction in stiffness of flexion compression for dynamic device, compared with the rigid device. Conclusion The dynamic device offers a design that may enhance load sharing without sacrificing the stability and will decrease stress shielding and stress concentration.